There has been proposed a fluidized bed gasification system for gasification of raw material such as coal, biomass or sludge wherein raw material is supplied to a fluidized bed gasification furnace preliminarily supplied with hot bed material or fluid medium, a gasification agent being supplied to form a fluidized bed to thereby gasify the raw material, resultant produced gas being taken out outside while the bed material and char produced upon the gasification in the gasification furnace are supplied to a fluidized bed combustion furnace for heating of the bed material through fluidized combustion of the char, the heated bed material being supplied again to said fluidized bed gasification furnace (see, for example, Reference 1).
FIG. 1 shows a fluidized bed gasification system disclosed in the above Reference 1. In FIG. 1, reference numeral 1 denotes a fluidized bed combustion furnace into which the bed material and char produced upon gasification of raw material 26 in a fluidized bed gasification furnace 2 are introduced from below, air supplied from an air pipe 4 being blown through a bottom wind box 3. The char and bed material are fluidized and raised by the blown air and are burned and heated, respectively, while they are raised. Reference numeral 5 denotes a supplementary fuel port for supplying supplementary fuel for heating to a fluidized bed in the fluidized bed combustion furnace 1; 6, a heat exchanger for heat recovery arranged in an upper portion of the combustion furnace 1.
The upper portion of the fluidized bed combustion furnace 1 is connected through a transfer pipe 7 to a separator 8 comprising a cyclone. The separator 8 has outer and inner cylinders 9 and 10, hot fluid including bed material from the fluidized bed combustion furnace 1 being introduced via the transfer pipe 7 tangentially into the outer cylinder 9 where it is centrifuged into the bed material and exhaust gas. The exhaust gas with fine-grained ash is discharged through the inner cylinder 10 while the bed material 11 with rough-grained unburned char is supplied to a fluidized bed gasification furnace 2 via a downcomer 12 extending downward from a lower end of the outer cylinder 9 in the separator 8.
The fluidized bed gasification furnace 2 comprises an introductory portion 13 for introduction of the bed material 11 separated in the separator 8 through the downcomer 12, a gasification portion 15 for gasification of raw material 26 from a raw material supply device 14 through heat of the bed material 11, a communicating portion 17 for supply of the bed material 11 in the introductory portion 13 through a fluidized bed 16 to the gasification portion 15 and a gasification agent box portion 18 extending over bottoms of the portions 13, 17 and 15 for supply of the gasification agent such as steam into the fluidized bed gasification furnace 2 and connected with a gasification agent supply line 19. The separation of the introductory and gasification portions 13 and 15 in the fluidized bed 16 by the communicating portion 17 as shown in FIG. 1 prevents the burnt gas in the fluidized bed combustion furnace 1 from flowing back through the fluidized bed gasification furnace 2 into the separator 8.
The bed material and the char not gasified in the gasification portion 15 are supplied for circulation to the fluidized bed combustion furnace 1 via a supply flow passage 25 comprising for example an overflow pipe, the bed material being then heated again by the combustion of the char.
When coal is supplied as raw material 26 to be gasified to the gasification portion 15, produced is produced gas 20 mixed with gas components such as hydrogen (H2), carbon monoxide (CO) and methane (CH4); when biomass or the like with a high water content is supplied as raw material 26 to be gasified, produced is produced gas 20 with the above-mentioned gas components containing much steam. The produced gas 20 is taken out via a discharge pipe 21 from the fluidized bed gasification furnace 2 into a recovery device 22 where the produced gas 20 is separated from impalpable powder 23 having been entrained in the gas and is taken out through an inner pipe 24. The produced gas 20 thus taken out may be pressurized and supplied as fuel to, for example, a gas turbine, or may be supplied to a refinery for production of any target gas from the produced gas 20.
[Reference 1] JP 2005-41959A